A white paper released last week examines the recent uptick in highway death statistics (view stats) and attempts to answer the question of what is to blame for the negative trend. Michael Sivak, a research professor at the University of Michigan Transportation Research Institute, examined the various explanations commonly offered and concluded economic factors appear to be the most important.

His analysis begins with an attempt to understand the massive drop in road fatalities between 2005 and 2011. In just seven years, the raw number of road deaths plunged 26 percent to the lowest level since 1949. When the crash numbers looked positive, everyone wanted to attribute the good news to their own special projects.

"A lot of parties at the table are taking credit for this huge drop, including vehicle manufacturers, federal regulators, driver-licensing agencies, public-interest groups, etc," Sivak wrote. "Indeed, there is evidence that each of them has contributed to the drop. Examples of proven contributory factors include more frequent installations of and improvements in airbags, electronic stability control, and more effective graduated driver-licensing laws. However, as we argued two years ago, looming in the background is another important factor, the economic downturn."

Sivak argues the decrease in the number of vehicle miles traveled over during the recession has not been great enough to fully account for the fatality drop. He suggests more substantial changes in driving patterns, including lower speeds and a reduction in rural driving factor into the result. He cites the example of the recession cutting down on commerce, which meant fewer freight trucks hit the road. Having fewer heavy vehicles on the road makes driving safer because big trucks are responsible for a greater share of serious crashes. The variability of the accident numbers with the state of the economy is evidence that stability control and similar gadgets play a lesser role.

"The important aspect of these and other economic effects is that they are temporary," Sivak wrote. "Once the economy picks up, these effects will disappear or be greatly reduced. This is in contrast to permanent effects of technological advances in vehicles and of regulatory actions (if enforcement is maintained)."

According to National Safety Council data, road fatalities are up 8 percent in the first seven months of 2012. Sivak drew a number of lessons from his findings.

"Do not expect most regulatory actions aimed at drivers to produce a sudden, huge drop in fatalities," Sivak wrote. "This is the case because such actions usually target only a portion of drivers (such as improvements in graduated driver licensing targeting young drivers only). Resign yourself to the fact that any sudden, large reduction in fatalities is likely only an unintended by-product of factors that influence the entire transportation system, such as a rapid change in the economy. Be aware that most rapid, underlying changes are transient, and therefore their effects are mostly transient too."

A copy of the report is available in a 200k PDF file at the source link below.